1. Field of the Invention
This invention relates to knitting machinery and more particularly to a device which detects overtension and/or breakage in thread.
2. Prior Art
Devices for detecting excessive tension and breakage of threads in textile machinery are known in the prior art. Typically, these devices of the prior art are comprised of two detection levers pivotally mounted on a case, the first detection lever being arranged and configured to detect the breakage of thread, while the second lever is arranged and configured to detect excessive tension in the thread. In these known devices, the first detection lever includes a counterweight which, if and when the thread breaks, causes a pivoting thereof to occur. Such pivoting provides the indication of thread breakage. The second detection lever typically includes a coil or spiral spring which resiliently maintains it in a proper position to hold the thread so long as the tension on the thread is not excessive. However, when the tension on the thread becomes excessive, the second detection lever pivots to an angular position which enables the thread to escape therefrom before breaking.
The devices of the prior art have several significant limitations and shortcomings which the present invention overcomes. For one thing, in most of the known devices, the tension of the spring used in connection with the lever for detecting excessive thread tension increases too rapidly as the detection lever pivots, so that very often, the thread breaks before the lever assumes the angular position which would enable the thread to escape. When this occurs, the operator must join together the ends of the broken thread and restart the machine, causing a delay in operation. The present invention substantially precludes the breakage of thread, even relatively thin thread, due to the rapid increase of spring tension as the second detection lever pivots.
A second shortcoming of some of the devices of the prior art results from the manner in which the spring is connected to the lever for detecting excessive thread tension. Often, this spring is placed in such a position that the detector lever, if it passes beyond a certain balance point in the course of its pivoting movement, tilts suddenly to a fully open position in which it is maintained by the tension of the spring. For this reason, when over-tension in the thread is detected and the thread escapes, it is necessary, before restarting the machine, to reset the detection lever to its closed position, in addition to the usual replacement of the thread. However, the resetting of the detection lever is often difficult to carry out inasmuch as it is typically located at a relatively great height on the knitting machine. Thus, its resetting requires the use of manually manipulated long pole or stick (in addition to the pole or stick required to replace the thread). The requirement for an additional pole or stick to reset the detection lever, or the need for a specific pole or stick adapted to enable both the replacement of the thread and the resetting of the detection lever is a significant disadvantage of these known devices. Moreover, the requirement to reset the detection lever causes a further delay in the restarting of machine operation.